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marcus

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Two more papers on the "bounce cosmology" theme (#4 on our list of six) appeared yesterday.

http://arxiv.org/abs/1501.06591

S.D. Odintsov, V.K. Oikonomou, Emmanuel N. Saridakis

(Submitted on 26 Jan 2015)

We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R), F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of different effective gravities which realize the above two bouncing cosmologies, indicates to some universality lying behind such a bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.

31 pages.

http://arxiv.org/abs/1501.06270

Jaume Haro, Jaume Amorós

(Submitted on 26 Jan 2015)

It is shown that teleparallel F(T) theories of gravity combined with holonomy corrected Loop Quantum Cosmology (LQC) support a Matter Bounce Scenario (MBS) which is a potential

6 pages. Communication to the FFP2014 (Frontiers in Fundamental Physics, Marseille 2014). To appear in

Also it may be recalled that the example given for this theme was the "LambdaCDM Bounce" paper by Cai and Wilson-Ewing, and the latter author will be presenting this work at two meetings in February:

On Thursday, 12 February at the Erlangen Cosmology and Quantum Gravity Workshop.

And then the next week on Wednesday 18 February at the Tux EPI Winter School.

Bounce cosmology often dispenses with inflation and it may be a

http://arxiv.org/abs/1501.06591

**Superbounce and Loop Quantum Ekpyrotic Cosmologies from Modified Gravity: F(R), F(G) and F(T) Theories**S.D. Odintsov, V.K. Oikonomou, Emmanuel N. Saridakis

(Submitted on 26 Jan 2015)

We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R), F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of different effective gravities which realize the above two bouncing cosmologies, indicates to some universality lying behind such a bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.

31 pages.

http://arxiv.org/abs/1501.06270

**Matter Bounce Scenario in F(T) gravity**Jaume Haro, Jaume Amorós

(Submitted on 26 Jan 2015)

It is shown that teleparallel F(T) theories of gravity combined with holonomy corrected Loop Quantum Cosmology (LQC) support a Matter Bounce Scenario (MBS) which is a potential

**alternative to the inflationary paradigm.**The Matter Bounce Scenario is reviewed and, according to the current observational data provided by PLANCK's team, we have summarized all the conditions that it has to satisfy in order to be a viable alternative to inflation, such as to provide a theoretical value of the spectral index and its running compatible with the latest PLANCK data, to have a reheating process via gravitational particle production, or to predict some signatures in the non-gaussianities of the power spectrum. The calculation of the power spectrum for scalar perturbations and the ratio of tensor to scalar perturbations has been done, in the simplest case of an exact matter dominated background, for both holonomy corrected LQC and teleparallel F(T) gravity. Finally, we have discussed the challenges (essentially, dealing with non-gaussianities, the calculation of the 3-point function in flat spatial geometries for theories beyond General Relativity) and problems (Jeans instabilities in the case of holonomy corrected LQC or local Lorentz dependence in teleparallelism) that arise in either bouncing scenario.6 pages. Communication to the FFP2014 (Frontiers in Fundamental Physics, Marseille 2014). To appear in

*Proceedings of Science*

Also it may be recalled that the example given for this theme was the "LambdaCDM Bounce" paper by Cai and Wilson-Ewing, and the latter author will be presenting this work at two meetings in February:

On Thursday, 12 February at the Erlangen Cosmology and Quantum Gravity Workshop.

And then the next week on Wednesday 18 February at the Tux EPI Winter School.

Bounce cosmology often dispenses with inflation and it may be a

**more natural alternative**to inflation. The singularity has to be replaced by something, and quantum GR-based models often seem predisposed to replace it with a bounce. If one accepts what quantizing GR offers, then, one does not have to invent mythical "inflaton" fields in order to get the observed cosmic features. So this theme increasingly comes up in the research literature.
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